Abstract : It was confirmed that the mammalian Cerebral Cortex contains principles which are able to inhibit the pituitary-adrenal axis of the rat. Semi-purified materials having this type of activity were obtained using chromatography on Sephadex G25 and G15, on columns of carboxy-methyl-cellulose (CMC) and ion exchange chromatography on IRC 50. More purified fractions have been obtained using high voltage electrophoresis. It has been shown in addition that the frontal part of the bovine Cerebral Cortex contains principles stimulating rather than inhibiting the pituitary-adrenal axis. The work performed measuring CRF in the hypothalamus of animals submitted to 'hypothalamic deafferential' indicates that the mechanism through which Cerebral Cortex principles influence the pituitary-adrenal axis is via an effect on this hypothalamic Releasing Factor. (Author)